Optical recording media known in the art include compact discs (“CDs”), recordable CDs (“CD-R”), rewritable CDs (“CD-RW”), write-only CDs (“CD-WO”), and digital video discs (“DVDs”). An optical recording medium is typically comprised of multiple layers that are compressed and adhered together. The bottom layer is a transparent substrate or support layer. Overlying the bottom layer, in ascending order, are a recording layer, a light reflective layer, and a protective layer. The optical recording medium is comprised of two surfaces, a data surface and a non-data surface. The data surface contains the information recorded onto the optical recording medium. The information is read by exposing the data surface to a laser. The non-data surface generally includes the protective layer and any images printed onto that layer.
The most common method of identifying the contents of the optical recording medium is to mark the case in which it is stored. This is typically accomplished by including printed material in the case. However, if the optical recording medium is ever separated from its case, the contents of the optical recording medium can not be easily identified.
The non-data surface of the optical recording medium may also be marked so that the contents of the optical recording medium may be easily identified. For example, images, such as text or graphics, may be printed on the protective layer by a variety of techniques. The least expensive method of marking the optical recording medium is to manually mark on the medium with a writing instrument. However, this method presents a number of problems. First, the method is not permanent because the writing may smear or fade over time. In addition, the amount of information that can be marked on the medium is limited by the nib size of the pen and the user's handwriting. Furthermore, the ink of the writing instrument may damage the underlying layers of the medium or interfere with the reading of the data surface. Finally, the writing instrument itself may damage the protective layer if it has a hard tip.
Another inexpensive method of marking is to apply labels marked with identifying images to the optical recording medium. However this method is disadvantageous because the amount of information that may be stored on the label is limited by the nib size of the writing instrument, the user's handwriting, and the size of the label. In addition, if the labels are not perfectly centered, they may affect the rotation of the optical recording medium, thereby causing read errors. Labels known in the art include symmetrical, doughnut-shaped labels and asymmetrical labels. Furthermore, if the label is ever removed, the adhesive may remove and damage portions of the underlying layers, causing additional problems with rotation of the optical recording medium or reading of the same.
More expensive methods of marking optical recording medium include printing images on the protective layer. The images may be printed by screen-printing, ink-jet printing, or wax transfer printing. These printing techniques require expensive printers and, typically, are only economical when commercial quantities of the optical recording medium need to be marked with identical information. The most common method of marking optical recording medium is screen-printing. Screen-printing utilizes an ultra-violet (“UV”)-curable ink or coating that is applied over the protective layer. Typical UV-curable coatings comprise resins that can be polymerized (such as acrylates), pigments, and photoinitiators. The UV-curable coatings may also contain additional resins to modify the viscosity, adhesion, and gloss properties of the coatings. UV-curable coatings are known in the art and are commercially available from Coates Bros. PLC (Kent, Great Britain) or Coates Inc. (USA). The UV-curable coating is applied over the protective layer and must bond thereto. The UV-curable coating is cured by exposure to a UV-light source, which initiates polymerization of the acrylates, causing them to form a hard, non-smearable coating on the optical recording medium. UV-curable coatings are available in various colors, so that multi-color text or graphics may be marked on the optical recording medium.
While multiple methods of marking optical recording medium exist, the methods vary in the permanence of the marks, the specialized equipment that is required, and the amount of information that can be marked. In view of the shortcomings in the art, there is a need for a method of permanently marking optical recording medium that does not require specialized equipment and that allows increased amounts of information to be marked.